Your computer is an important energy consumer in your home. Can you save
energy when using it? This article offers a few tips.
1. Buy a voltmeter
You only know how much electricity you use if you have a way to measure
it. And only if you measure it can you minimize its use. A voltmeter
gives you this ability. You can buy one for only $25 US at Amazon.
A popular inexpensive Voltmeter
You plug the voltmeter into the wall socket, then plug the device you
want to measure into the voltmeter. To measure how much electricity all
your computer equipment uses, plug it all into a power
strip, and plug the power strip into the voltmeter.
If you’re like me, when you get your new voltmeter you’ll run
around the house and measure the power consumption of everything in
sight. You’ll quickly find ways to minimize your use of electricity,
powering off some appliances and using others less. With your computer you’ll discover:
How much electricity your system uses depends on the device type, the power
consumption of the processor and motherboard, the number and type of
memory sticks, how many disk drives, what peripherals you have, etc.
Your computer uses less electricity at idle than when in use, and heavy
use drives the power consumption higher than light use. Heavy
disk I/O and maximum CPU utilization use more power, for example.
2. Use a laptop instead of a desktop. Or a tablet or smartphone.
It’s tough to generalize about computer power
consumption because it varies so widely. (That’s why you bought the
voltmeter!) Most desktop computer systems consume between 70 and 200
watts while in use, while laptops often burn between 15 and 60 watts. Both figures include typical LCD displays. View this power consumption chart to see how much electricity some typical systems use. This chart lists power consumption for displays alone.
A laptop in use always uses less electricity than a desktop in use.
Often by a pretty significant ratio. If you’re buying a computer and
you’re into saving
electricity, go with a laptop. I’ll show you a formula below so you can
easily determine the energy cost savings you get with a laptop. (We’re
only talking ongoing energy consumption here. We’re ignoring factors like
whether laptops last as long as desktops, how much energy goes into
their production, etc.)
If they meet your needs, consider moving to even more energy-stingy devices,
like tablets or smartphones. (Here are example power specs for the iPad and iPhone.) From least to greatest energy consumed, the device type hierarchy is:
3. Use a flat panel display instead of a CRT monitor
Those big, bulky old CRT monitors use several times the power of
space-saving, power-sipping flat panel displays. CRT’s often consume
between 60 and 110 watts, while most flat panels are down in the 15 to
60 watt range. No contest!
The energy savings you’ll get might even pay you to buy a flat panel to
replace an old CRT. You can calculate this yourself. Here’s how.
My old Dell D1028L 17″ CRT used about 100 watts of power, while my beautiful replacement Acer P205H 20″ LCD/TFT display uses only 28 watts (and only 0.75 watts at Standby!).
Say I use the computer for 4 hours per day every day. Here’s the electricity calculation for these two displays:
Electric bills measure your usage in thousands of watts per hour, or
kilowatt-hours. So the comparison is between 146 kWh versus 40.88 kWh.
Your electric bill shows what your power company charges per kWh. Mine
happens to be 15 cents per kWh. Just multiply it out:
So I save $21.90 – $6.13 or $15.77 a year by using the LCD instead of
the CRT. If the Acer costs me about $120, I can divide $120 by $15.77 to
determine that it will pay for itself in under 8 years solely from
electric bill savings.
The financial experts out there will point out I’m ignoring amortization,
inflation, and lord knows what else, but this simple calculation
suffices for most of us. Use it to compare
/ 1000) * charge per
kilowatt-hour = total electricity cost
Laptop versus Desktop — Redo
Let’s use the formula to compare laptop to desktop energy costs.
Say I want to replace a Dell OptiPlex GX260 Pentium 4 and its 17″
Dell LCD display from 2003 with an Apple MacBook Pro with
15″ integral display from 2010. The Dell desktop and its
display together consume 104 to 162 watts during moderate use. I’ll
assume 135 watts here. The MacBook clocks in at 55 to 58 watts for
moderate use. I’ll assume 55 watts.
We’ll again assume 4 hours of moderate use per day, or 1,460 hours
annually. At 135 watts/hour, the Dell desktop consumes roughly 197.1
per year. At 55 watts/hour the laptop consumes around 80.3 kWh per
Assuming 15 cents per kWh, that prices the desktop’s annual electrical
bill at about $29.56 and the laptop’s at $12.05. The difference is
$17.51. I can use this number to help me decide whether buying
the laptop is
I’ve made many assumptions here but the approach is valid. Use it
to compare electrical costs. Remember that we’re excluding other
factors like the energy used during manufacture, longevity (MTBF),
disposal costs, etc.
4. Set your Power Management options
Measurements with your new voltmeter quickly expose a power
consumption hierarchy. These are your computer’s power usage levels,
from greatest power consumption to least:
Use -> Idle -> Standby ->
Hibernate or Turned Off
A heavily-used computer sucks more power than one at idle, while idling requires more power than standing by or hibernating.
There’s lots of confusion between the terms standby, sleep, and hibernate.
For good reason. How they work vary by operating system and by computer
manufacturer! There is no industry-standard meaning for these terms.
I’ll use the U.S. Department of Energy definitions. These recognize two distinct states: hibernate and standby.
Hibernate means the computer
saves its state, then turns itself off. It will reload its state when
you turn it on again. Hibernate powers up faster than a regular boot.
The computer uses zero power during hibernation.
Standby means the computer still uses power but at a reduced level.
Non-essential components are powered down. The computer can “awake”
faster than from hibernate mode but uses some minimal power to enable
this. This chart summarizes:
|Energy Use:||1 to 5 watts||0 watts||0 watts|
|Time to Become Usable:||quickest (under 5 seconds)||intermediate (30 seconds to 2 minutes)||longest (2 or 3 minutes)|
U.S. DOE definitions for Standby and Hibernate. Figures are approximate.
One quick word about screen savers. Many don’t
save energy. That’s not their purpose. They may even use more
electricity if they’ve got color graphics moving all around. (Pick the
“Blank screen” as the most energy efficient screen saver.) To save
either turn off your display or set its power management options.
To set your computer’s Power Management options, in Windows you can right-click on the desktop,
select Properties, then choose the Screen Saver tab. Here you set the screen saver attributes. Click on the Power button to set the power management options. In Ubuntu go to System -> Preferences -> Screensaver. You can click on the Power Management button from there.
Typical Linux Screen Saver and Power Management Panels (from openSUSE 11.4)
Always test your power management settings. It’s not unusual to find quirks in how they work (or
don’t). This is doubly true if the operating system you’re running was
Beyond OS-based power management, you can also install an intelligent power calibration tool like Granola. This free Windows & Linux product does dynamic voltage and frequency scaling (DVFS) for your system’s CPUs. MiserWare’s web site claims Granola can reduce your computer’s
electrical use from 15% to 35%. Monitor with your voltmeter over a
period of time to see what results you get.
How much electricity can you save by proper power management? It depends on how you use your computer. This study
cranks real numbers for office workers and finds that reducing annual
energy consumption by 80% is not unusual. I think that what this means is
that going from ignorance of power management to active power
management is a huge win.
5. Turn off your computer when you’re done for the day
From a power consumption standpoint, a computer turned OFF always uses less power than one that is still ON.
Some claim that the power required to start up a computer is greater
than that consumed by leaving the computer on overnight. Not
true. The power involved in start-up is about the same as power
consumed during maximum regular use (“heavy use”). Measure it
with your voltmeter. Or view the proof in this chart. The extra
power consumed at start up will not exceed the power used by keeping
the computer on all the time. Even if the computer is in standby status, which consumes just a few watts per hour.
This research study gives you the numbers on this and concludes that “… ensuring computers are turned off at night dramatically reduces their energy consumption.”
Some claim that starting a computer “stresses it” due to a “power
surge” and makes it more likely to fail sooner. They say you should
leave your computer on overnight rather than switching if off and on.
Majority opinion among those who seriously research the issue is that “Hard
drives and other components are now better built, so wear and tear through
daily powering on and off of desktop computers is no longer a consideration.”
The U.S. Department of Energy has
it right for most of us:
technology long before the effects of being switched on and off multiple
times have a negative impact on their service life. The less time a PC
is on, the longer it will “last.” PCs also produce heat, so turning
them off reduces building cooling loads.”
Of course, if you need your computer on at night to perform work,
that’s a whole different story. Some people perform updates or run
batch processes overnight. Just set your power management options so
that they take effect after the work completes.
6. Use an Ink Jet printer and turn it on only when printing
energy consumption varies widely. You’ll have to use your voltmeter to
see how much electricity yours draws when printing and when turned on
From least to greatest energy consumed printer technologies order like this:
Since dot matrixes are largely
obsolete due to lesser print quality, this makes the ink jet is the best
energy-conscious choice for most home users. An active laser printer uses several times more electricity than your computer!
Most home users only print occasionally. You can save
electricity by turning on the printer only when you intend to print,
then turning it off immediately afterwards. Don’t leave it on all the
time. Some people waste electricity because they
put their printer on the same powerstrip as their computer so it’s on
whenever their computer is on. Energy savings will be dramatic for
laser printers, which consume hundreds of watts when active and tens of
in standby mode.
7. Buy Energy Star equipment
Energy Star (or ES) is a joint program
run by the U.S. Department of Energy and the Environmental Protection
Agency. Computer equipment that meets ES energy efficiency standards display the Energy Star logo:
The Energy Star Logo
Many countries beyond the U.S. have adopted the ES system
and at least 40,000 appliances conform to it. Energy Star specs cover
all kinds of computer components including system units, power
supplies, batteries, displays, printers, and more. What’s great about
that the program is strictly voluntary. It does not impose
government regulation. Yet it saves billions of dollars per year in
energy costs while minimizing our carbon footprint. The EPA estimates
ES saved $14 billion in energy costs in 2006 alone.
The first ES specification for computer equipment was developed in
1992. The current computer specification is version 5.0 from 2009. The good news is that the ES specs keep moving
forward and incrementally improving. The bad news is that the changes
make it hard to compare power efficiency between systems released under
different ES standards. ES is a great
tool for buying new energy efficient hardware. It isn’t so useful when
comparing hardware across time.
How much will you save by buying Energy Star products? This
article calculates a total lifecyle
savings for a computer system of $161, or 18% of the initial purchase
price. Even if that’s on the high side, it pays to buy ES!
8. Keep your computer in service longer
In my articles on
computer refurbishing I advocate keeping computers in
service until either technological obsolescence or their natural end of
life. Some readers have responded that this is a bad idea because older
computers consume more electricity than newer ones. Actually, if you’re
talking consumer systems produced over the past decade, there has been
but minor reduction in operational energy consumption in spite of the ES energy
efficiency increases. You can’t take a random new computer and assume it uses
less electricity than one from 2005 or even 2000. The big change for
consumer systems has
displays. Not only do LCDs use way less energy
than CRTs, but newer flat panel displays use less than older ones.
The key reason to keep consumer computers in service longer is environmental. It costs both natural resources and energy to make a computer. Lots. If your current machine
still does the job, replacing it with a new computer
of the same type (desktop or laptop) unnecessarily consumes resources.
According to a United Nations University study, the natural resources that
go into making a computer are about 10 times its weight in fossil
fuels and and chemicals, versus only 1 to 2 times their weight for a
car or refrigerator. This is why your little laptop is so expensive compared to larger appliances in your house.
Then there’s the huge problem
of proper disposal of all the toxins computers contain when they’re no longer usable.
What about energy? This research project found it takes about 1,778 kWh of electricity to produce a desktop
computer and monitor as of 2004. This is as much energy as the typical
in two months. It’s enough energy to keep your 100 watt desktop in
active use for 17,780 hours. That’s over 12 years of daily use at 4
hours per day. Given
a typical lifespan
of 3 to 5 years, this means that the energy cost to produce a computer
greatly exceeds the energy it consumes during its operational
This article underscores the point. Based on research recently published in the Journal of Cleaner Production, it concludes that “Computer factories eat way more energy than the devices they build.” The study found that 70% of the energy a typical
laptop will consume during its life span is used in manufacturing the
If you buy two computers of the same type
or laptop) over a decade, you use less total energy than if you had
bought three in
same time span. The best way to reduce your computer
energy use is to buy fewer computers. This is why research from sources as diverse as Fujitsu and the Gartner Group advocate device longevity.
What if you replace a device of one type with a device of another
type that consumes less electricity?
example, say you replace your old desktop with a new laptop or a
say you replace your laptop with a smartphone. Now you have a much more
complicated comparison. I’ve shown in this article how to compute ongoing
electrical costs. You can use the simple formula to predict and compare your electrical bills for different devices.
haven’t compared the energy required to manufacture different kinds
of devices. Nor have we explored how recycling costs might differ for
device types. And these are just two of the factors you’d have to
measure to make an accurate judgement.
For now let’s stop at one useful conclusion. So long
as it still does
the job you need done, it is cheaper to keep your current computer
service than it is to replace it with a similar new one.
This is true both from the standpoint of the total energy cost (energy
cost to manufacture plus ongoing power consumption) and from the
standpoint of natural resource consumption.
Refurbishing and reusing computers in the 3 to 10 year old range is
without question good for the environment.
– – – – – – – – – – – – – – – – – – – – – –
Howard Fosdick (President, FCI) is an independent consultant who
databases and operating systems. His hobby is refurbishing computers as
a form of social work and environmental contribution. Read his other articles here or email him
at contactfci at the domain
name of sbcglobal (period) net.
great article, but there are more severe problems you can find with a wattmeter (not voltmeter as stated in the article)
and some times there are simple means to solve them
adding extra insulation to a boiler can reduce power-consumption significantly